The present invention relates to the field of electrosurgery, and more particularly to surgical devices and methods which employ high-frequency electrical energy to treat soft tissue in regions of the spine. The present invention also relates to improved devices and methods for the treatment of intervertebral discs
Intervertebral discs mainly function to articulate and cushion the vertebrae, while the interspinous tissue (i.e., tendons and cartilage, and the like) function to support the vertebrae so as to provide flexibility and stability to the patient's spine.
The discs comprise a nucleus pulposus which is a central hydrophilic cushion. The nucleus is surrounded by an annulus fibrosus or annulus which is a multi-layered fibrous ligament. The disc also includes vertebral endplates which are located between the disc and adjacent vertebrae.
The nucleus pulposus occupies 25-40% of the total disc cross-sectional area. It is composed mainly of mucoid material containing mainly proteoglycans with a small amount of collagen. The proteoglycans consist of a protein core having attached chains of negatively charged keratin sulphate and chondroitin sulphate. Such a structure is the reason the nucleus pulposus is a “loose or amorphous hydrogel” which has the capacity to bind water and usually contains 70-90% water by weight.
The annulus fibrosus forms the outer boundary of the disc and is composed of highly structured collagen fibers embedded in amorphous base substance also composed of water and proteoglycans. However, the amorphous base of the annulus is lower in content than in the nucleus. The collagen fibers of the annulus are arranged in concentric laminated bands. In each laminated band the fibers are parallel and attached to the adjacent vertebral bodies at roughly a 30° angle from the horizontal plane of the disc in both directions. There is a steady increase in the proportion of collagen from the inner to the outer annulus.
Each disc has two vertebral end-plates composed of hyaline cartilage. As mentioned above, the end-plates separate the disc from adjacent vertebral bodies. The end-plates act as a transitional zone between the harder bony vertebral bodies and the soft disc. Because the nucleus pulposus does not contain blood vessels (i.e., it is avascular), the disc receives most nutrients through the end-plate areas.
Many patients suffer from discogenic pain resulting from degenerative disc disease and/or vertebral disc herniation. Degeneration of discs occurs when they lose their water content and height, causing adjoining vertebrae to move closer together. The deterioration of the disc results in a decrease of the shock-absorbing ability of the spine. This condition also causes a narrowing of the neural openings in the sides of the spine which may pinch these nerves. Thus disc degeneration may eventually cause severe chronic and disabling back and leg pain.
Disc herniations generally fall into three types of categories: 1) contained disc herniation (also known as contained disc protrusion); 2) extruded disc herniation; and 3) sequestered disc herniation (also known as a free fragment.)
In a contained herniation, a portion of the disc protrudes or bulges from a normal boundary of the disc. However, in a contained herniation, the nucleus pulposus and the disc do not breach the annulus fibrosus, rather a protrusion of the disc might mechanically compress and/or chemically irritate an adjacent nerve root. This condition leads to radicular pain, commonly referred to as sciatica (leg pain.) In an extruded herniation, the annulus is disrupted and a segment of the nucleus protrudes/extrudes from the disc. However in this condition, the nucleus within the disc remains contiguous with the extruded fragment. With a sequestered disc herniation, a nucleus fragment separates from the nucleus and disc.
Degenerating or injured discs may have weaknesses in the annulus contributing to herniation of the disc. The weakened annulus may allow fragments of nucleus pulposus to migrate through the annulus fibrosus and into the spinal canal. Once in the canal, the displaced nucleus pulposus tissue, or the protruding annulus may impinge on spinal nerves or nerve roots. A weakened annulus may also result in bulging (e.g., a contained herniation) of the disc. Mechanical compression and/or chemical irritation of the nerve may occur depending on the proximity of the bulge to a nerve. A patient with these conditions may experience pain, sensory, and motor deficit.
A significant percentage of such patients undergo surgical procedures to treat the disorders described above. These procedures include both percutaneous and open discectomy, and spinal fusion.
Often, symptoms from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. Such treatments result in a gradual but progressive improvement in symptoms and allow the patient to avoid surgical intervention.
In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and preventing reoccurrence of the symptoms.
Until recently, surgical spinal procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. However, the development of minimally invasive spine surgery overcomes many of the disadvantages of traditional traumatic spine surgery. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuing scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open procedures. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Percutaneous techniques for the treatment of herniated discs include: chemonucleolysis; laser techniques; mechanical techniques, such as automated percutaneous lumbar discectomy; and Nucleoplasty using Coblation plasma technology. These procedures generally require the surgeon to place an introducer needle or cannula from the external surface of the patient to the spinal disc(s) for passage of surgical instruments or device. Open techniques for the treatment of herniated discs involve surgical dissection through soft tissue and removal of a portion of vertebral bone. Conventionally, upon encountering the annulus a complex surgical incision, called an annulotomy, must be made to allow access of instruments into the disc so that decompress the disc may take place. Mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like are often used to remove the nucleus material. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, and most significantly, the annulotomy itself may lead to future re-herniation of the disc or even accelerate disc degeneration. Discussion of the problems associated with the annulotomy is found in journals and other medical publications. (see e.g., Ahlgren, et al. Annular incision technique on the strength and multidirectional flexibility of the healing intervertebral disc., Spine 1994, Apr. 15; 9(8) pp 948-954; Ahlgren, et al. Effect of annular repair on the healing strength of the intervertebral disc: a sheep model., Spine 2000, Sep. 1; 25(17): pp 2167-2170.)
Previously, in order to reduce the risk of re-herniation of the annulus subsequent to the performance of an annulotomy, the surgeon removes an excess amount of nucleus material from the disc than that required to normally decompress the disc. However, it was found that removing an excess amount of the nucleus pulposus destabilizes the disc leading to accelerated disc degeneration. See e.g., Meakin et al., The Effect of Partial Removal of the Nucleus Pulposus from the Intervertebral Disc on the Response of the Human Annulus Fibrosus to Compression., Clin Biomech (Bristol, Avon) 2001 February; 16(2) pp. 121-128.
Monopolar and bipolar radiofrequency devices have been used in limited roles in spine surgery, primarily for hemostasis. Monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of undesirable electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Another significant disadvantage of conventional RF devices, particularly monopolar devices, is that the device causes nerve stimulation and interference with nerve monitoring equipment in the operating room. In addition, these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density increases the temperature of the cells causing cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” by exploding the cells along the pathway of localized tissue heating. Thus, while the tissue parts along the pathway of evaporated cellular fluid, the heating process induces undesirable thermal collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often includes indiscriminate destruction of tissue, resulting in thermal necrosis and the loss of the proper function of the tissue. In addition, the conventional device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to either encapsulate the zone with scar tissue or eventually remove the destroyed tissue via phagocytosis absorption.
A further problem with lasers and conventional RF devices is that the conduction of heat may cause unintentional damage to the vertebral end-plates. The vertebral end-plates contain chondrocytes which extract plasma and other nutrients from adjacent micro-capillaries to maintain the essential moisture and biochemistry within the disc. However, these chondrocytes are heat sensitive. Therefore, thermally damaging these chondrocytes may also destroy or impair the function of the vertebral end-plates thereby causing premature disc deterioration. In addition, damage of the end-plates may cause the adjacent formation of necrotic tissue, and/or thermal bone necrosis (i.e., a layer of dead bone), thereby creating a barrier to the passage of water and nutrients from the endplate into the disc. Such a condition may further accelerate the degeneration of the disc. The existence of necrotic tissue may also present problems if a fusion procedure is subsequently required. Any necrotic tissue at the site of the area to be fused must be removed or destroyed prior to fusion. Accordingly, the presence of necrotic tissue increases the duration of the fusion procedure and may adversely affect the outcome of the procedure.
Presently, there is a need for an improved treatment for individuals having disorders or abnormalities of an intervertebral disc. There is also a need to prevent disc herniations, especially extruded disc herniations and sequestered disc herniation (free fragments) when the annulus of the disc is weakened and/or diseased.
The methods and devices aimed at meeting the above needs should be applicable to all types of degenerative discs, and all levels of the vertebral column, including cervical, thoracic, and lumbar spine. Such methods and devices should also be applicable to all types of herniations.